| ??? 02/14/05 00:43 Read: times |
#87301 - three level output with resistors |
Hi, I am working with a 7 segment LCD, and trying to drive it with an 89s52. I had almost everything done, but I am having some dummy problem with the output levels...
As I have 2 different backplanes, I found a lot of AN's for other uC (PIC, Zilog, etc) that showed that by building a 3 level signal (0, 2.5 and 5 volts), with a different phase, it's possible to do all the stuff playing with signal phases, and TTL outputs. The main problem it's done with two resistors connected between two outputs. When both are high (or low), the output signal (measured between the resistors) is also high (or low). For the intermediate level, one must be high and the other low, and here is when the 51 collapses, as the low level pin sinks the other pin, and the result is always zero.... I managed to raise it a bit with a pull up, but can't get the right voltage level, and it gets more complicated when I mix the 2 backplanes ( I make them with 3 pins, for a smaller and simple code). I looked in many forums, I will read the bible to find out if there is a trick to do with pull ups/downs, but I'd like to know if anybody had dealed with this kind of situations before, and if there are succesfull cases ... Greetings Sebastián |
| Topic | Author | Date |
| three level output with resistors | 01/01/70 00:00 | |
| Buffer your pins... | 01/01/70 00:00 | |
| the advantage of '51 | 01/01/70 00:00 | |
| Try ATmega8515 | 01/01/70 00:00 | |
| or try a modern '51 | 01/01/70 00:00 | |
| ... and are not pin compatible... | 01/01/70 00:00 | |
| pin-compatible but reset is negative | 01/01/70 00:00 | |
| What is less pain? | 01/01/70 00:00 | |
| not any more | 01/01/70 00:00 | |
| where do you get your info? | 01/01/70 00:00 | |
| the horses mouth | 01/01/70 00:00 | |
| hmmmm | 01/01/70 00:00 | |
| pico gates, | 01/01/70 00:00 | |
| if just one unit or maybe | 01/01/70 00:00 | |
| 3 levels possible on 8051 without buffer | 01/01/70 00:00 | |
| the goalpost | 01/01/70 00:00 | |
| gotcha | 01/01/70 00:00 | |
The solution, but ... (almost off topic) | 01/01/70 00:00 | |
| A possible solution | 01/01/70 00:00 | |
| deja vu? | 01/01/70 00:00 | |
| Whoops! | 01/01/70 00:00 | |
| flat style | 01/01/70 00:00 | |
| aka | 01/01/70 00:00 | |
| R-2R | 01/01/70 00:00 | |
| R-2R? | 01/01/70 00:00 |